While single-mode fiber is a very efficient, low loss, lightwave transmission medium, and therefore used widely in applications like long haul communications where very low loss is a requirement, multi-transverse-mode optical fiber (hereinafter multimode fiber) fiber has an established status for short haul applications, and specialty fibers. For example, Local Area Network (LAN) applications have traditionally been based on low cost multimode fiber based systems. Such systems enable low cost by utilizing serial transmission, loose alignment tolerances between source and fiber end, and large alignment tolerances within connections and splices. To serve these applications effectively, the industry has set a standard for minimum acceptable transmission distance, and minimum optical fiber performance for that distance. The distance in current use is 300 meters for a single in-building optical link. In-building optical links comprise the vast majority of optical links in use today.
As data rates have increased to 10 Gb/s, the reach of traditional graded index multimode fibers is limited to distances of only 26 to 33 meters, using low cost multimode based serial systems.
In response to the need for faster transmission (10 Gb/s) rates over 300-m of MMF, the industry has responded and standardized a number of solutions. However, all of these solutions are unique and optimized for one wavelength. For example 10 GBE-SR is optimized for operation at 850-nm while 10 GBE-LX4 is optimized for operation at 1300-nm.
As the bandwidth demand continues to grow, it will be necessary to develop MMF that will transmit at speeds faster than 10 Gb/s. Likely, transmission rates are 40 and 100 Gb/s. Currently, a number of possible solutions are being considered. One solution is a 12×10 MMF parallel solution, where each of 12 fibers transmits at 10 Gb/s for a total transmission rate of 120 Gb/s over 12 fibers. Another possibility being considered is a wavelength division multiplexing (WDM) solution over MMF. It has been shown feasible that using current premium MMF one can transmit 10 Gb/s over 4 wavelengths over one fiber for a total transmission rate of 40 Gb/s. However, because current premium MMF are optimized at one wavelength (850-nm) and exhibit their peak bandwidth at one wavelength, expanding a WDM solution to more than 4 wavelengths with each channel transmitting 10 Gb/s is not currently possible.
Thus multimode fibers are needed that are optimized across broad wavelength ranges, coupled with appropriate laser launch conditions, for wavelengths to at least 300 meters, and data rates at 1, 10, and 100 Gb/s. The objective is to design fibers that maintain the present low cost for 1 or 10 Gbps at 850 nm, while opening up other wavelength bands for CWDM of 10 and 20 Gbps transmission. Ideally, one would like to transmit at least 10 wavelengths each operating at 10 Gb/s or faster for a total transmission rate of at least 100 Gb/s over a single MMF.
We have designed a new class of multimode optical fibers optimized for operation across broad wavelength ranges. These are aimed at applications using 1, 10 and 100 Gb/s data rates at 850 nm, as well as WDM solutions between 800 and 1300-nm at lengths of up to at least 300 meters.
The improved multimode optical fibers have cores doped with aluminum and/or phosphorus. In preferred embodiments they are doped with germanium and phosphorus, or germanium and aluminum. Optical fibers with these multiply doped cores are shown to provide the optical transmission qualities necessary to meet new standards for short haul optical fiber links. More details on these multiply doped optical fibers are set forth in U.S. application Ser. No. 11/511,174, which is incorporated by reference herein.
However, we have also observed that, while these optical fiber designs provide very effective solutions for low cost, high performance, multimode fiber applications, some optical fibers with phosphorus and/or aluminum doping have high sensitivity to hydrogen contamination. Thus the long term aging qualities of fiber doped with phosphorus and/or aluminum may limit the effectiveness of these optical fibers for some applications, unless a solution can be found. We have identified a solution in the present invention.